Project: Are Eastern Tropical Pacific reefs becoming more resilient to ENSO?

Description from NSF award abstract:
The predicted 2014-2015 El Niño Southern Oscillation (ENSO) event may develop into one of the strongest in recent history, presenting a unique and urgent opportunity to investigate the impact of this extreme thermal anomaly on the resilience of coral reef ecosystems. Building on baseline data from >40 years of research in the Eastern Tropical Pacific (ETP), this team of researchers is uniquely poised to test hypotheses about coral reef resilience to the third strong event to hit this region. Ecological resilience is defined as both the ability of an ecosystem to continue functioning while under stress as well as the ability of a system to "bounce back" or restore structure and function following a disturbance. This project is guided by the overarching hypothesis that many ETP coral reefs are becoming more resilient in the face of multiple major ENSO disturbances as a result of adaptive processes. If the investigators are correct that reef systems can develop more tolerance and recover more rapidly when subjected to sequential thermal disturbances, this will drastically change predictions of the fate of global coral reef ecosystems over the next 100 years of climate change.

This RAPID funding will provide an unprecedented opportunity to further our understanding of the potential for increased resistance to, and accelerated early recovery from, the third major ENSO to hit the ETP. The investigators have developed hypotheses that can be tested by targeted sampling and experiments in the critical stages before, during and after this ENSO on reefs in Panamá (Uva, Saboga) and Galápagos (Darwin Floreana). These reefs span a gradient in aragonite saturation that provides a real-world model system for conditions expected throughout the tropics in a high-CO2 world. Key mechanisms/hypotheses that the investigators will evaluate that may increase resilience, and therefore reduce mortality and limit the loss of ecosystem functioning following this ENSO, include: (1) increases in the relative abundance of thermotolerant symbionts will result in higher survival and faster recovery of multiple coral species across all depths; (2) recovery will be inversely rated to pCO2 with a threshold level beyond which recovery does not occur; (3) the maintenance of strong top-down control by intact herbivore communities will limit algal proliferation, and (4) the strengthening of nutrient-limitation in shallow regions will limit algal competitive abilities and aid coral recovery. At each site where there is a record of recovery the research team will make the following ovservations: (1) in situ measurement of physical parameters (temperature, conductivity, pH, dissolved oxygen, photosynthetically active radiation, chlorophyll, turbidity, inorganic nutrients); (2) in situ measurement of carbonate chemistry and net ecosystem metabolism (calcification, production); (3) In situ measurements of coral and reef community responses including coral bleaching and mortality and the population responses of corallivores, bioeroders, herbivores, and benthic algal cover; (4) quantification of symbiont communities in major coral species before, during and after the bleaching event to compare with archived samples from the 1997-98 event; (5) bioassays of the strength of top-down (herbivory) and bottom-up (nutrient limitation) effects that may promote ecosystem resilience with critical limits. To further explore these limits, in the southern Galápagos, where there is a lack of resilience, the investigative team will deploy temperature loggers, conduct surveys of bleaching and mortality of remnant coral communities, and conduct bioassays of the strength of herbivory and nutrient limitation.